cpeptide_params: C-peptide parameters estimates from population data

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C-peptide parameters estimates from population data

Description

cpeptide_params returns a dataframe with C-peptide kinetic parameters from population data. These parameters are commonly used for calculation of Insulin Secretion Rates. Based on the regression models from Van Cauter et al. Participants were considered "Obese" in this study if body weight was >15% above ideal body weight, rather than a commonly used BMI cutoff. The parameters can be used in calculations to estimate insulin secretion rates, shown in the example.

Usage

cpeptide_params(
  age,
  gender = NA,
  height,
  weight,
  category = "normal",
  weight_units = "kg",
  height_units = "m"
)

Arguments

age	Age in years
gender	Gender
height	Height in meters
weight	Weight in kg
category	Category ("Normal", "Obese", "NIDDM")
weight_units	weight units, if not in kg
height_units	height units, if not in meters

Value

Data frame with variables cp_vd, cp_halflife_short, cp_halflife_long, cp_fraction, cp_bsa, cp_k12, cp_k21, cp_k10

Usage Notes

Parameter notation: the kinetic parameter notation (k12, k21, k10) differs from the original Van Cauter notation, and metabolic modeling papers often vary in their notation. I have used the standard pharmacokinetics notation so that k12 indicates rate of movement from compartment 1 to compartment 2 (see Gibaldi & Perrier).

Results

Parameters included in the output dataframe include the prefix cp_ which is intended to aid in variable selection:

• cp_vd C-peptide Volume of Distribution (L)

• cp_halflife_short C-peptide "short" half life (minutes)

• cp_halflife_long C-peptide "short" long life (minutes)

• cp_fraction Weighting factor for short/long half-life

• cp_bsa Body surface area (m^2)

• cp_k12 C-peptide Rate constant (plasma -> tissue), 1/min

• cp_k21 C-peptide Rate constant (tissue -> plasma), 1/min

• cp_k10 C-peptide Rate constant (plasma -> elimination), 1/min

Basal Insulin Secretion Calculation

The simplest calculation uses k10 and vd to estimate basal insulin secretion: Basal~Insulin~Secretion~(pmol/min) = k_{10} \cdot V_d \cdot C-peptide(nM)*1000 If C-peptide has already been converted to pmol/L, then do not multiply by 1000. See examples for calculation example.

Examples

library(tabletools)
cpeptide_params(age=28.1, height = 1.744666, weight = 69.4, gender = "F", category = "normal")
cpeptide_params(age=28.1, height = 1.744666, weight = 69.4, gender = "M", category = "normal")
cpeptide_params(age=35.2, height = 1.678461, weight = 107.9, gender = "F", category = "obese")
cpeptide_params(age=35.2, height = 1.678461, weight = 107.9, gender = "M", category = "obese")

library(dplyr)
dat <- data.frame(id =1:10,
  age = rnorm(10, 50, sd=8),
  gender = sample(c("M", "F"), 10, replace = T),
  height = rnorm(10, 1.7, sd=0.2),
  weight = rnorm(10, 100, sd=20),
  cpeptide_0 =  abs(rnorm(10, 2.0, 0.91))  ) # ng/dL

dat |>
  mutate(ibw = calculate_ibw(height, gender, height_units = "m", weight_units = "kg"),
         ibw_pct = (weight/ibw-1)*100,
         ibw_15 = case_when(ibw_pct>15 ~ "obese", # if >15% above IBW then Obese
                            TRUE ~ "normal"),
         cpeptide_0_pmol = convert_cpeptide_to_pM(cpeptide_0, cpeptide_units="ng/ml"),
         cpeptide_params(age, gender, height, weight, category = ibw_15),
         # Basal Insulin Secretion Rate (pmol/min)
         ISR_0 = cp_k10*cpeptide_0_pmol*cp_vd)

JMLuther/tabletools documentation built on April 14, 2025, 3:09 a.m.